Surface Water Supply Index Maps and Reports

The Surface Water Supply Index (SWSI) is designed for areas that rely on snow melt as the primary source of surface water. The SWSI accounts for snowpack, mountain precipitation, streamflow, reservoir storage, and soil moisture conditions. The SWSI is used by irrigators, fisheries specialists, recreationalists, and others to evaluate current and seasonal surface water supplies. SWSI maps and reports are available for each month from January through October beginning in 1992.

View a map by choosing the month and year of interest from the dropdown box or by selecting from the thumbnails below. Asterisk (*) denotes missing map.

These maps are produced in partnership with the NRCS. Data are compiled by the Montana
Snow Survey Program of the USDA Natural Resources Conservation Service. Please see
the NRCS web site for explanations of their data collection programs.